The invention relates to an operation controller for an air conditioner capable of varying the number of revolutions of a compressor thereof in accordance with the air conditioning load.
FIGS. 20 to 24 show a conventional air conditioner disclosed in, e.g., Japanese Examined Publication No. 12532/1985. FIG. 20 is a block diagram showing a configuration of the conventional air conditioner; FIG. 21 is a front view of a panel portion of a display operation section of the conventional air conditioner; FIG. 22 is a characteristic diagram showing a relationship between temperature differences and zones in the conventional air conditioner; and FIG. 23 is a time chart showing an operation of the conventional air conditioner. In FIG. 20 , a power supply 1 supplies ac power to a rectifier circuit 2, where the ac power from the power supply 1 is rectified to dc power. The dc power outputted from the rectifier circuit 2 is applied to a frequency converter 3. The frequency converter 3 can continuously convert the output frequency in the range of from about 25 to 80 Hz by a digital control signal, thereby varying the rotational speed of a compressor 4 in the range of from 1400 to 4500 rpm. On the other hand, the digital control signal applied to the frequency converter 3 is outputted by a controller 5. The controller 5 applies to a microprocessor (not shown) an operation signal outputted from a display operation section 6, a signal of an ambient temperature detected by a temperature sensor 8, and a signal of a cooling medium condensing temperature detected by a temperature sensor 9 to operate a load 7 such as a four-way valve and a fan motor by executing arithmetic and logic operations in accordance with predetermined programs. At the same time, the controller 5 delivers a set frequency signal to the frequency converter 3 and displays operation conditions of the compressor 5 on an LED display panel on the display operation section 6.
As shown in FIG. 21, the display operation section 6 includes: a bar display 11 that displays the number of revolutions of the compressor 4 in the form of performance level; a temperature setting unit 12 that sets the ambient temperature and outputs a temperature set signal; a selector switch 13 that selects the intensity of an inside fan (not shown) and outputs a fan intensity set signal; an operation stop switch 14 that stops the operation of the air conditioner; selector switches 15, 16 that switch between the cooling and the heating operation of the air conditioner and output an operation instruction signal; and display LEDs 17, 18 that display the operation conditions of the cooling or the heating operation of the air conditioner.
As described above, the temperature set signal of the temperature setting unit 12 and the fan intensity set signal of the selector switch 13, and operation instruction signals of the operation stop switch 14, the selector switches 15, 16, all being outputted from the display operation section 6, are applied to the controller 5.
The controller 5 is mainly formed of a microcomputer, and is designed to operate in correspondence to microcomputer programs. Accordingly, the controller can output with ease a set frequency signal in accordance with the difference between an ambient temperature detected by the temperature sensor 8 and a temperature set by the temperature setting unit 12, so that the number of revolutions of the compressor 4 is controlled so as to match the air conditioning load.
While an exemplary correspondence between differences between ambient temperatures and set temperatures and frequency set signals are shown, operation conditions thereof will be described with reference to FIGS. 22 and 23. As shown in FIG. 22, the variable range of differences between ambient temperatures and the set temperatures and of differences in frequency set signal is divided into six (6) zones A to F for each of the cases where ambient temperatures (or differences between ambient temperatures and set temperatures) depict a downward gradient and an upward gradient. More specifically, when the ambient temperature is in the downward gradient region X, a range in which the ambient temperature is 1.degree. C. or more higher than the set temperature is designated as zone A, a range in which the ambient temperature is 0.5.degree. to 1.0.degree. C. higher than the set temperature is designated as zone b, a range in which the ambient temperature is 0.degree. to 0.5.degree. C. higher than the set temperature is designated as zone C, a range in which the ambient temperature is 0.degree. to 0.5.degree. C. lower than the set temperature is designated as zone D, a range in which the ambient temperature is 0.5to 1.0.degree. C. lower than the set temperature is designated as zone E, and a range in which the ambient temperature is 1.degree. C. or more lower than the set temperature is designated as zone F.
When the ambient temperature is in the downward gradient region Y, a range in which the ambient temperature is 1.5.degree. C. or more higher than the set temperature is designated as zone A, a range in which the ambient temperature is 1.0.degree. to 1.5.degree. C. higher than the set temperature is designated as zone B, a range in which the ambient temperature is 0.5.degree. to 1.0.degree. C. higher than the set temperature is designated as zone C, a range in which the ambient temperature is 0.degree. to 0.5.degree. C. higher than the set temperature is designated as zone D, a range in which the ambient temperature is 0.degree. to 0.5.degree. C. lower than the set temperature is designated as zone E, and a range in which the ambient temperature is 0.5.degree. C. or more lower than the set temperature is designated as zone F. Here, zone D is particularly designated as a control target zone. These temperature ranges and frequency set signals are made to correspond as shown in FIG. 24. Such correspondence means that if the difference between the ambient temperature and the set temperature is in zone A, the controller 5 applies a frequency set signal of 75 Hz to the frequency converter 3, whereas if the difference between the ambient temperature and the set temperature is in zone F, the controller 5 applies a compressor stop instruction to the frequency converter 3. FIG. 23 shows changes in ambient temperature expressed in terms of differences between the ambient temperature and the set temperature when the air conditioner is driven for cooling, together with changes in frequency. In FIG. 23, when the difference between the ambient temperature and the set temperature is in zone A (1.0.degree. C. or more), the ambient temperature at which a frequency set signal of 75 Hz is applied is decreased rapidly. When the difference moves to zone B (less than 1.0.degree. C.), a frequency set signal of 65 Hz is applied to the frequency converter 3. As the difference sequentially drops to be found in zone D, a frequency set signal of 45 Hz is applied to the frequency converter 3. As long as the ambient temperature is in the downward gradient as described above and is maintained lower than the set temperature by 0.degree. to 0.5.degree. C., the frequency set signal of 45 Hz is continuously applied. If the ambient temperature is so increased afterwards that the ambient temperature is higher than the set temperature by 0.degree. to 0.5.degree. C., then the ambient temperature now belongs to the upward gradient zone D. Thus, a frequency set signal of 45 Hz is similarly applied continuously.
More specifically, since there is a difference of 0.5.degree. C. between the ambient temperature and the set temperature in the downward gradient, this difference acts as a hysteresis. Once the ambient temperature has reached the target temperature, the air conditioning operation is performed with no frequent change in the set frequency taking place.
Since the operation controller for the conventional air conditioner determines the operation frequency of the compressor so that the operation frequency matches an ambient load, if the load is small, the controller operates the air conditioner at the minimum frequency at all times. And this does not ensure that the air conditioner is always operated at the operation frequency of optimal efficiency.